Geosteering Diagnosis: A New Approach to Monitor the Well Position Within a 3D Geological Model

Abstract

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractWith the increasing demand for more efficient drilling operations, the oil industry is searching for new ways of utilizing all data available while drilling. The integration of the realtime drilling information with data from offset wells and the reservoir model is considered of high value for accurate wellbore placement and geosteering. This paper introduces an original methodology to better understand and analyze the well position within the subsurface and to warn the end user when predefined geological and drilling events are appearing or prognosed ahead of the drill bit. The concept is called Geosteering Diagnosis. We identify a monitored trajectory as composed of a real-time and a project-ahead section. The bit and the MWD/LWD sensors are monitored objects attached to the trajectory. A number of targeted objects (i.e. horizons, contacts, faults, targets, planned and previous drilled wells trajectories, well and grid properties) are accessible from the 3D geological model. Rules can be defined based on the relationship between the monitored objects and any targeted objects. Various thresholds are used to identify events at the time of the drilling and alarms can be triggered on specific cases. The Geosteering Diagnosis is applied to a production well in the North Sea. The rules are used to monitor drilling against the predefined geological model. They provide quantitative information, which can be used to either update the geological model, or take actions regarding the course of the well.